A modern gas turbine engine, such as is used for generation of electricity at power plants, is a multi-part assembly of sub-components, many of which are subjected to vibrational and thermal stresses over long periods of operation. To the extent that various sub-components and their respective parts are designed, manufactured, shipped and installed to reduce undesired stresses, this may result in longer operation and less downtime.
In common configurations of gas turbine engines, a plurality of combustors is arranged radially. Compressed air flows through these combustors, including through, in each such basket, one or more fuel/air mixing devices (such as swirler assemblies), and then through a combustion zone. The combustion zone begins after a barrier, such as a base plate, that demarcates an upstream end of the combustion zone. The combustion zone may terminate before or may extend into what is referred to as a “transition piece” (alternatively referred to as a “tail pipe,” “transition duct,” or “combustion tube” by some in the field, partly depending on the elements upstream to this). The transition piece is a conduit that carries hot gases into a turbine where the gases effectuate movement of turbine blades and thereby turn a rotor, such as to generate electricity.
A common approach to assembly of a transition piece with a combustor in a gas turbine engine is to attach at a downstream end (in terms of operation and direction of gas flow) of the combustor an assembly of spring clips. U.S. Pat. No. 4,413,470 (the '470 patent), issued Nov. 8, 1983 to Scheihing and Laurelli, describes a spring clip ring assembly at a downstream end of a combustor that provides sliding support that accommodates thermal growth by a catalytic unit. A second spring clip ring is used to establish a relationship between a catalytic unit and a transition piece. FIGS. 11-15 of the '470 patent depict, and the associated text describes, spring clip assemblies, or rings, that respectively each comprises a plurality of spring fingers (referred to as spring clips herein). This patent is incorporated by reference for its teachings of spring clips and their assembly in a combustor. In addition, this and all other patents, patent applications, patent publications, and other publications referenced herein are hereby incorporated by reference in this application in order to more fully describe the state of the art to which the present invention pertains, to provide such teachings as are generally known to those skilled in the art.
Further as to combustors and their operation, the general operation of main swirler assemblies and pilots are known in the art of can-annular gas turbine engine combustion and operation. For example, aspects of this technology are described in U.S. Pat. No. 6,732,528, issued May 11, 2004 to Akagi and Tomimoto. Also, aspects of the functioning of a transition piece (and, depending on the reference, to other aspects of a gas turbine engine) are disclosed in the following U.S. Pat. No. 4,719,748, issued Jan. 19, 1988 to Davis et al.; U.S. Pat. No. 4,903,477, issued Feb. 27, 1990 to Butt; U.S. Pat. No. 6,463,742, issued Oct. 15, 2002 to Mandai et al.; and U.S. Pat. No. 5,906,093, issued May 25, 1999 to Coslow and Whidden.
As one example of combustor structure, FIG. 1A provides a side partial cut-away view of a particular prior art combustor 100 of a gas turbine engine with an upstream end 102, a downstream end 104, and an assembly 108 of spring clips 112 affixed to the downstream end 104. A plate 114 at the upstream end 102 provides a structure for attachment of the combustor 100 to another structural member (not shown) of the gas turbine engine. Bracing ribs 116 are attached to the plate 114 and extend downstream along the exterior of the combustor 100. Also viewable in FIG. 1A through the cut-away section is a central pilot 120 about which a plurality of main swirler assemblies (e.g. six or eight, not viewable in FIG. 1A) is arranged.
FIG. 1B provides a side view of the encircled area of FIG. 1A, providing more details of the assembly 108 of spring clips 112. The non-compressed state of the most forward-shown spring clips 112 is exhibited by showing distance ‘a,’ and spaces 109 are shown between adjacent spring clips 112. Location 115 identifies one of a plurality of spot welds of the spring clips 112 to an outer frame 118 of combustor 100. The spot welds extend circumferentially around the combustor 100. Also, it is observable that the assembly 108 is comprised of an inner layer 110 and an outer layer 111 of spring clips 112.
FIG. 1C provides an upstream end view of the assembly 108 of spring clips 112 further showing the inner layer 110 and the outer layer 111. These layers 110 and 111 are shown without other components, and are shown offset to one another, so that the spaces 109 are not aligned. This offset arrangement of the spaces 109 reduces passage of gases during operation.
FIG. 1D provides a side partial cut-away view of the prior art combustor 100 of FIG. 1A joined in operational position with a prior art transition piece 150. The transition piece has an upstream end 152, and a downstream end 154 that connects to an entrance of a turbine (not shown). The upstream end 152 has a circumferentially extending transition inlet ring 156 which is disposed over the assembly 108 of spring clips 112. FIG. 1E provides an enlarged view of the area encircled in FIG. 1D, to better show aspects of and the relationships between the spring clips 112 and the transition inlet ring 156.
Further referring to FIG. 1E, the transition inlet ring 156 compresses spring clips 112, as evidenced by a distance ‘b’ that is smaller than uncompressed distance ‘a’ of FIG. 1B. That is, the inside diameter of transition inlet ring 156 is less than the outside diameter of the uncompressed spring clips 112 as depicted in FIG. 1A. This compression aids in achieving a desired tightness of fit at this junction during operation, when there is vibration from combustion and other forces, as well as high temperature from combustion gases.
Having recognized the causes of certain problems associated with the spring clips, such as those described above, the present inventors have conceived solutions that address one or more problems related to shipping, installation, repair and operational incidents pertaining to these springs on a gas turbine engine combustor.